Germ cell development in D. melanogaster is a powerful model system to study questions concerning the genetic and molecular mechanisms involved in tissue formation. Individual genes and molecular pathways that are involved in Drosophila germ-line formation will most likely have homologues in humans. These developmental pathways can be used as starting points to investigate the defects of inborn and acquired diseases of human germ tissue. The tudor gene product is one of eight known genes necessary for germ cell formation to occur in D. melanogaster. It codes for a protein 2515 amino acids long without significant homology to known proteins or structural motifs. Molecules that bind to the Tudor have not yet been identified. Therefore, to determine Tudor binding molecules and define their function in germ cell development the following specific aims will be pursued: 1. What are the proteins binding to Tudor? Known and unknown proteins will be screened for binding to Tudor using the yeast two-hybrid system, cDNA expression libraries probed with radiolabelled recombinant Tudor proteins, and purification from embryo lysates. 2. Is Tudor a novel RNA-binding protein? Known co-localizing RNAs and those prepared from purified polar granules will be tested for direct interaction using in vitro binding techniques. 3. What is the function of Tudor binding proteins and RNAs? Established Drosophila techniques will be used to determine the role of the identified interacting proteins and RNAs in germ cell development and to investigate other potential functions of Tudor.